SHSAT: Punctuation: commas, colons, semicolons and apostrophes
Learn to set off extra information with a pair of commas, use colons and semicolons where they belong, and form possessives and its correctly.
How do you decide which punctuation mark a sentence needs?
Short answer
Ask what the mark is doing. Commas come in pairs around extra information, a colon follows a complete sentence, semicolons separate list items that already contain commas, and an apostrophe shows ownership, with its never taking one.
Know first: Complete sentences and clauses, Singular and plural nouns
Step 1 of 6
Extra information gets a pair of commas
Some phrases add extra information about a noun that is already identified. Remove the phrase and the sentence still says exactly who or what you mean. Extra information is set off with two commas, one before it and one after.
Other phrases are essential: they tell you which one. The students who finished early may leave means only those students. Essential phrases take no commas.
If there is only one of something, such as my mother or our school's gym, a phrase about it can't be identifying it, so it is extra.
Wrong: Our school nurse, Ms. Diaz keeps a spare umbrella.
Right: Our school nurse, Ms. Diaz, keeps a spare umbrella.
Ms. Diaz renames the nurse, so it is extra information and needs a comma on both sides. The closing comma is the easy one to forget.
Step 2 of 6
Other marks follow fixed rules
| Mark | Rule | Example |
|---|---|---|
| Colon | Comes after a complete sentence, before a list or explanation | The kit has two tools: a wrench and a file. |
| Semicolons in a list | Separate items that already contain commas | Austin, Texas; Reno, Nevada; and Erie, Pennsylvania |
| Plural possessive | Add an apostrophe after the s | the girls' lockers |
| Irregular plural possessive | Add 's to the plural | the men's team |
| Its and it's | Its shows ownership; it's means it is | The dog wagged its tail. |
| Quotation | A comma goes inside the closing quotation mark | “We're late,” Kim said. |
| Direct address | Set off the name of the person spoken to | Jo, please close the door. |
| Subject and verb | No comma between them | The box of old maps belongs here. |
A colon never comes right after a verb or a preposition: The kit has: a wrench is wrong.
Step 3 of 6
Use the removal test on a real choice
Worked example: Extra or essential?
Our town has one public pool. Which sentence punctuates the extra information correctly?
- AThe town pool which opens in June needs a new diving board.
- BThe town pool, which opens in June, needs a new diving board.
- CThe town pool, which opens in June needs a new diving board.
- DThe town pool which opens in June, needs a new diving board.
- 1
Is it extra?
The town has one pool, so the town pool already identifies it. Which opens in June only adds information.
- 2
Count the commas
Extra information needs two commas. Only B has both.
- 3
See why the others are there
A treats the phrase as essential, as if the town had several pools. C drops the closing comma. D drops the opening comma and puts a comma between the subject and its verb.
Answer
B. The town pool, which opens in June, needs a new diving board.
Find the wrong step
A student fixes Bring three things on the trip, a hat, water and a snack.
- 1
Notices that the list explains what the three things are.
- 2
Decides a colon can't follow a command, so leaves the comma after trip.
What went wrong
A command is a complete sentence, so a colon can follow it. The comma lets the list run into the sentence.
- 3
Moves on to the next question.
The fix
Bring three things on the trip: a hat, water and a snack.
Step 4 of 6
Check what each mark is doing
Check yourself · Question 1
Choose the correct phrase for bikes that belong to several women.
Answer: B
Women is already plural and doesn't end in s, so add 's: women's.
Check yourself · Question 2
Which sentence uses a colon correctly?
Answer: C
The recipe needs three ingredients is a complete sentence, and the colon introduces the list that explains it.
Check yourself · Question 3
Mia's school has many teachers. Which sentence correctly says that only the teachers who coach a sport get the new jackets?
Answer: D
The phrase tells which teachers, so it is essential and takes no commas.
Trap answer: The teachers, who coach a sport, get the new jackets.
Correct-looking commas, wrong meaning
- Why it looks right
- A pair of commas around a who phrase looks like the textbook pattern.
- Why it's wrong
- Commas mark the phrase as extra, so the sentence says all the teachers get jackets. The writer means only some of them.
- The right answer
- No commas, because the phrase identifies which teachers.
Common mistake
I put a comma wherever I'd pause when reading aloud.
- Why it's tempting
- Commas often match pauses, so your ear seems like a good guide.
- Do this instead
- Long subjects make you pause before the verb, but a comma can't go there. Decide by the comma's job: extra information, list items, an introductory element or a joining word.
Step 5 of 6
What to remember
Remember
- Use the removal test: extra information takes a comma on both sides, and essential information takes none.
- A colon follows a complete sentence; semicolons separate list items that already contain commas.
- Plural possessives add an apostrophe after the s, irregular plurals add 's, and its never takes an apostrophe.
Step 6 of 6
Practice on a real question
Use what you just learned on this question, then check the explanation.
In your own words
In the practice question, how did knowing the speaker has exactly one sister tell you whether the phrase was extra or essential?